Abrasive articles are frequently used in microfinishing applications such as semiconductor wafer polishing, microelectromechanical (MEMS) device fabrication, finishing of substrates for hard disk drives, polishing of optical fibers and connectors, and the like. For example, during integrated circuit manufacture, semiconductor wafers typically undergo numerous processing steps including deposition of metal and dielectric layers, patterning of the layers, and etching. In each processing step, it may be necessary or desirable to modify or refine an exposed surface of the wafer to prepare it for subsequent fabrication or manufacturing steps. The surface modification process is often used to modify deposited conductors (e.g., metals, semiconductors, and/or dielectric materials). The surface modification process is also typically used to create a planar outer exposed surface on a wafer having an exposed area of a conductive material, a dielectric material, or a combination.
One method of modifying or refining exposed surfaces of structured wafers treats a wafer surface with a fixed abrasive article. In use, the fixed abrasive article is typically contacted with a semiconductor wafer surface, often in the presence of a working fluid, with a motion adapted to modify a layer of material on the wafer and provide a planar, uniform wafer surface. The working fluid may be applied to the surface of the wafer to chemically modify or otherwise facilitate the removal of material from the surface of the wafer under the action of the abrasive article.
Fixed abrasive articles generally have an abrasive layer of abrasive particles bonded together by a binder and secured to a backing. In one type of fixed abrasive article, the abrasive layer is composed of discrete raised structural elements (e.g., posts, ridges, pyramids, or truncated pyramids) termed shaped abrasive composites. This type of fixed abrasive article is known in the art variously by the terms “textured, fixed abrasive article” or “structured abrasive article” (this latter term shall be used hereinafter).
In order to assess progress during the planarization process it is common practice to use various detection methods. Optical detection methods (e.g., laser interferometry) are among the most widely used. In such techniques, a laser is typically directed through windows in a platen and a subpad in contact with the structured abrasive article. A hole or transparent (uncoated with abrasive layer) portion of the structured abrasive article is aligned with the beam.